BLOCK AT A GLANCE
Blockade of the four terminal branches of the sciatic nerve and the saphenous nerve (optional) at the level of the distal leg and ankle.
Indications: Distal foot and toe surgery, transmetatarsal or toe amputations
Goal: Local anesthetic (LA) spread surrounding each individual nerve
Local anesthetic volume: 3 to 5 mL per nerve
The ankle block is a commonly performed regional anesthesia technique for procedures on the forefoot. Traditional techniques based on surface landmarks and nerve stimulation targeted the two deep nerves (tibial and deep peroneal) and required an additional subcutaneous ring infiltration around the ankle to block the three superficial nerves (superficial peroneal, sural, and saphenous). Ultrasound (US) guidance allows for precise identification of each nerve and a consistent blockade using lower volumes of LA. The quality, duration, and distribution of the blocks around the ankle are similar to those of more proximal approaches of the sciatic nerve.
The main advantage of the ankle block is the preservation of ankle mobility and thus facilitation of unassisted ambulation.
Limitations and Specific Risks
The main limitation is due to the fact that it requires multiple injections; the time required to complete the blockage is longer. An ischemia tourniquet at the level of the ankle is well-tolerated even with an ankle block. However, additional sedation or anesthesia is required for more proximal locations of the tourniquet. Specific complications of the ankle block are extremely rare.
The tibial nerve is the largest of the five nerves at the ankle level and provides innervation to the intrinsic muscles, bones, joints, and skin of the heel and sole of the foot. The nerve passes posterior to the medial malleolus, in close contact to the posterior tibial artery and veins, deep to the flexors retinaculum, where it divides into the calcaneal, medial, and lateral plantar nerves (Figure 32-1).
Relative position of the terminal nerves at the level of the ankle.
The deep peroneal nerve crosses the anterior surface of the ankle, deep to the tendons of the tibialis anterior, extensor hallucis longus muscles, and extensor digitorum longus next to the anterior tibial artery. The nerve enters the foot to innervate the extensor digitorum brevis and extensor hallucis brevis muscles and all the deep structures on the dorsum of the foot. It terminates as cutaneous fibers supplying skin between the hallux and second toe (Figure 32-1).
The superficial peroneal branch emerges at 10 to 20 cm proximal to the lateral malleolus to lie superficial to the crural fascia between the lateral and anterior muscular compartments, at 10 to 20 cm proximal to the lateral malleolus. It divides into two or three small branches and terminates as ...